1. Field of the Invention
This invention relates to a liquid crystal display device and a method for manufacturing the same, and more particularly to a liquid crystal display device in an in-plane switching system and a method for manufacturing the same.
2. Description of the Related Art
In an active matrix type liquid crystal display device, the in-plane switching system in which the direction of the electric field to be applied to liquid crystal is in parallel to a substrate has been adopted mainly as a technique for obtaining a very wide angular field of view (See JP-A-8-254712). It has been confirmed that this system can practically remove changes in the contrast when the direction of view angle is changed and in inversion of a gradation level (See M. Oh-e et al, “Asia Display” '95, pp. 577-580). FIG. 7 is a plan view of a pixel region of a conventional general in-plane switching liquid crystal display device. In FIG. 7, reference numeral 100 denotes a TFT (Thin-Film-Transistor) array substrate, and 200 a CF (Color Filter) substrate. Reference numeral 1 denotes one of gate wirings which are a plurality of scanning signal lines formed on an insulating substrate, 2 a gate insulating film, 3 one of source wirings, 4 an insulating film formed on each of the source wirings, 5a, 5b common electrodes, and 6 one of pixel electrodes.
In the IPS liquid crystal display device, the pixel electrodes 6 and common electrodes 5 opposite thereto are arranged on the TFT array substrate. By the electric field between the pixel electrode 6 and common electrode 5, the liquid crystal is driven in the direction of the TFT array substrate. In the configuration shown in FIG. 7, a driving voltage is supplied to the pixel electrode 6 through the TFT so that the electric field is generated in a direction in parallel to the gate wiring 1, i.e., perpendicular to the source wiring 3. By the electric field between the pixel electrode 6 and common electrode 5, the light from a backlight unit provided on the rear side of a liquid display panel is selectively transmitted thereby to provide a desired image.
Referring to FIGS. 8A and 8B, an explanation will be given of the problem involved with the IPS liquid crystal display device described above. FIG. 8A is a plan view which schematically shows the structure of the IPS liquid crystal display device. FIG. 8B is a sectional view which shows the structure in the vicinity of the gate terminal part. FIGS. 8A and 8B schematically show the entire configuration of the liquid display panel and a BM (black matrix) arranged thereon. In FIGS. 8A and 8B, reference numeral 10 denotes a liquid display panel, 11 a display region, 12 a frame region, 13 gate terminal part, 14 source terminal part, 15 a BM (black matrix), 17 a sealing member, 100 a TFT array substrate, and 200 a CF (color filter) substrate.
Generally, the active matrix liquid crystal display panel includes the TFT array substrate 100, CF substrate 200, which is smaller than the TFT array substrate 100, and liquid crystal layer 18 sandwiched therebetween. The TFT array substrate 100 and CF substrate 200 are bonded to each other by the sealing member 17. TFTs (Thin Film Transistors) are arranged in a matrix shape on the TFT array substrate 100. As shown in FIG. 7, the TFT which is a switching element is provided for each of the pixels. On the CF substrate 200, a coloring layer (not shown) is formed at a position corresponding to the pixel for which the corresponding TFT is provided.
A collection of the areas where the pixels are formed constitutes a display region 11 and its periphery constitutes a frame region 12. In the frame region 12 of the TFT array substrate 100, the gate terminal part 13 and source terminal part 14 are formed. The gate terminal part 13 and source terminal part 14 are formed at the ends along the sides of the TFT array substrate 100 adjoining each other, respectively. Namely, the gate terminal part 13 is formed at the end along one end of the TFT array substrate 100, and the source terminal part 14 are formed at the end of the side adjoining the one side. Gate driver ICs for supplying scanning signals are connected to the gate terminal part 13, and source driver ICs for supplying display signals are connected to the source terminal part 14. The signal from each driver IC is supplied to the gate wiring or source wiring through the terminal formed on the gate terminal part 13 or source terminal part 14.
Generally, between the CF substrate 200 of the liquid crystal display device and the coloring layer, light shielding films called “BM” (black matrix) of resin is formed. Further, in the IPS liquid crystal display device, since the source wirings provided on an upper layer shield the backlight, apart of the BM can be omitted. In such an IPS liquid crystal display device, as shown in FIGS. 8A and 8B, a line-like light shielding films 15 are formed. These shielding film 15 are formed in a direction in parallel to the gate wirings, i.e. direction perpendicular to the side where the gate terminal part 13 is provided.
In the IPS liquid crystal display device, since the pixel electrodes and common electrodes are formed on the TFT array substrate 100, the CF substrate 200 is provided with no transparent electrode. Therefore, the light shielding films 15 formed on the CF substrate 200 is not electrically shielded, but capacitively coupled with the gate wirings. As a result, when the electric field is applied to the liquid crystal panel, the electric charge distribution of the light shielding films 15 changes. Thus, the electric field between the pixel electrodes and the common electrodes is disturbed. Such a disturbance of the electric field gives rise to crosstalk or after-image, leading to deterioration in the display quality.
Particularly, changes in the gate potential in the gate terminal part 13 when a signal is inputted to the liquid crystal display panel spread to the light shielding films 15 so that the liquid crystal is instantaneously oriented in a direction of the substrate. As a result, the pixels in the vicinity of the gate terminal part 13 temporarily make white display. In the charge distribution in the light shading films 15 which has been disturbed by the changes in the gate potential, since the charges are diffused over the entire panel from the side of the gate terminal part 13, the region of the white display disappears instantaneously. However, if any wire break occurs in the light shielding films 15, only the broken line(s) looses an escape of charges on the side of the gate terminal. This generates an emission line (s), thereby reducing the production yield.
The liquid display device for obviating such an inconvenience has been proposed (See JP-A-2000-10107 (FIG. 4)). In this liquid display device, a slit is provided on the resin BM in the direction in parallel to the side where the signal is extracted. Thus, the liquid display device can prevent the changes in the gate potential in the gate terminal part from spreading to the BM in the display region. Thus, even the BM is broken, it is possible to prevent the occurrence of the emission line.
However, where the slit in the BM is provided, light leakage occurs at the portion where the slit is provided. In order to prevent the light leakage in the slit in the BM, the slit is arranged on a bus line at the potential equal to that at an opposite electrode. Therefore, the width of the bus line is increased by the slit width (e.g. 100 μm). This gives rise to a problem that the parasitic capacitance is increased to deteriorate the display quality. Further, at the slit, the light incident from the side of the display plane is reflected toward the display plane in a metallic pattern of the bus line. As described above, in the conventional IPS liquid crystal display device, it is difficult to keep the BM potential in a suitable status without influencing the display quality so that the afterimage and display unevenness are reduced.
As described above, the conventional IPS liquid crystal display device has presented a problem that it is difficult to keep the BM potential in a suitable status without influencing the display quality so that the afterimage and display unevenness are reduced.